1. Field of the Invention
The invention relates to an electrode substrate and a producing method thereof, particularly an electrode substrate with an excellent electrical stability used for liquid-crystal display elements, organic electro-luminescence elements (organic EL elements) and the like and a producing method thereof.
2. Description of the Background
Conventionally cathode ray tubes (CRT) have been generally used as a display means. However liquid-crystal display elements, which have advantages such as thin type, light weight and energy saving, have been practically used and widely used in personal computers and the like.
Display means of spontaneous self-emitting type such as organic EL elements, inorganic EL elements and plasma displays have been researched and developed as a display means of next generation in place of CRTs.
These display means has demanded an electrode substrate with an excellent electrical stability that enables the driving by low voltage for a long period of time.
For example, Japanese Patent Kokai No. 11-295747 proposes a liquid-crystal display element in which a resist mask for etching remains as it is in stripe electrodes made of an ITO film on a transparent substrate.
The object of the electrode substrate is to prevent the occurrence of display defects due to disconnection by protecting the ITO film, which is a transparent electrode. However, the surface state of electrode has not been considered and its electrical stability cannot be sufficiently improved.
Japanese Patent Kokai No. 11-305248 proposes a liquid-crystal display element of refection and transmission combined type that has a transmission electrode part and reflection electrode part on pixel electrodes on a transparent substrate. The transmission electrode part is made of a transparent electrode film such as ITO. The reflection electrode part is made of a reflective electrode film such as Al.
The object of the reflection electrode part is to prevent the reduction of contrast and improve the visibility in both transmission and reflection modes. However, the surface state of electrode has not been considered and its electrical stability cannot be sufficiently improved.
Japanese Patent Kokai No. 11-133447 proposes an electrode substrate in which an ITO film is formed on a surface of a transparent substrate. The transparent substrate has a refractive index of 1.4 to 1.6. The ITO film has a refractive index of 1.65 to 1.95 in the visible light band and an optical film thickness of about λ/2 times the wavelength of light source beam used.
This electrode substrate can prevent reflection for light of a wide wavelength region. However, the surface state of electrode has not been considered and its electrical stability cannot be sufficiently improved.
Japanese Patent Kokai No. 11-126689 proposes an electrode substrate obtained by subjecting a substrate used for an organic EL element to inverse sputtering by a RF sputtering device before the formation of a transparent electrode film so that the maximum surface roughness of the substrate is smaller than 15 nm and the average roughness is smaller than 10 nm.
The document teaches that the preferred distance between the substrate and target is form 4 to 15 cm in this method, since an ordinary RF sputtering device is used in inverse sputtering.
The object of the electrode substrate of Japanese Patent Kokai No. 11-126689 is to improve the surface roughness of substrate and therefore the electrical connection on an electrode formed on a substrate. However the composition and the binding state of atoms in the surface of electrode are not considered. Thus, when driving the organic EL element for a long period of time, the driving voltage excessively increases so that the electrical stability cannot be sufficiently improved.
In addition, the distance between the substrate and target is narrow, since an ordinary RF sputtering device is used. As a result, it is difficult to change the conditions of inverse sputtering.
Therefore, in order to solve the above problems, objects of the present invention are to provide an electrode substrate with an excellent electrical stability by associating the surface composition of electrode with its interior composition; reduce surface defects by improving an electrode itself by inverse sputtering and the like; and specifically provide a method for efficiently producing electrode substrates with an excellent electrical stability while reducing surface defects in the electrode surface.